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An Ancillary Rain Accumulation Data Product to Assess the Effects of Rain on the Remote Sensing of

Sea Surface SalinityAndrea Santos-Garcia1, Shadi Aslebagh1, Maria Marta Jacob2 and Linwood Jones1

1 Central Florida Remote Sensing Laboratory, University of Central Florida2 Comisión Nacional de Actividades Espaciales

AbstractTo date, both AQ and SMOS missions have observed significant differences between L-band SSS retrievals in presence of rain and surface truth (buoys andHYCOM model). Based upon pre-launch analyses of rain effects, this is an unexpected result, which begs the question “Is it retrieval error or science?”In an attempt to resolve this issue, an AQ Rain Accumulation product has been developed to overlaps the Aquarius L2-SSS data. It is derived from theTropical Rainfall Measuring Mission (TRMM) 3B42 product, which is a near-global, gridded rain rate dataset that extends from ±50° latitude and isproduced 8 times daily at 0Z, 3Z, 6Z . . . and 21Z (3-hr windows). Based upon the AQ pixel observation time, these 3B42 data are temporally interpolatedin 3-hr windows and spatially averaged over each AQ IFOV to produce a rainfall history during the previous 24hrs. A beta version of this ancillary rainfallproduct is available to the AQ science team at JPL PODAAC.The purpose of this paper is to describe this AQ Rain Accumulation product and to present validation results using independent WindSat rain retrievals(EDR) that occur within ± 45 minutes for ~60% of the AQ L2 science data pixels.

0 no observation1 AMSU2 TMI3 AMSR4 SSMI5 SSMI/S6 MHS7 TCI30 AMSU/MHS avg31 Conical scanner avg50 IR

3B42 PRODUCT

DATA SOURCE

EVERY 3 HOURS

TIME FREQUENCY

0 HRS

3 HRS

6 HRS

21 HRS

AQ RAIN ACCUMULATION – SOURCE DATA

TIME DIFFERENCE TO THE CENTER OF THE TIME WINDOW DATA SOURCE

INSTANTANEOUS RAIN RATE FROM 3B42 @ 3 HOURS

Time difference

Source Flag

INSTANTANEOUS RAIN RATE FROM 3B42

Time difference

Source Flag

EARTH GRIDDED AQ IFOV (0.25°resolution)

3B42 DATA PRODUCT(ORIGINALLY @ 0.25°resolution)

DATA SETS ARE COLLOCATED

TIME INTERPOLATION OF 3B42 TO THE AQ OBSERVATION TIME

COLLOCATED DATASET

LINEAR TIME INTERPOLATION OF 3B42 IN 0.25 HR TIME STEPS

INSTANTANEOUS RAIN RATE (RR) @ AQ OBSERVATION

TIME

RAIN ACUMULATION RA

0 – 3 hrs 3 – 6 hrs 6 – 9 hrs 21 – 24 hrs

AQ RAIN ACCUMULATION ALGORITHM

0

1

2

3

4

5

INSTANTANEOUS RAIN RATE OVER AQ FOOT PRINT

0

5

0

5

0

5

0

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0

INSTANTANEOUS RR

RAIN ACCUMULATION PRODUCT OVER PREVIOUS 24 HOURS TO AQ TIME

0

1

2

3

4

5

RA03RA06

RA15RA12

RA09

RA24RA21

RA18

[mm

/hr]

CONCLUSIONSValidation performed using the well-calibrated WindSat EDRdata ensures reliability to the AQ RA productAQ RA product is a useful source of ancillary data thatpermits more comprehensive analysis of the rain effect onthe measurement of sea surface salinityAn improved version of the AQ RA product is underdevelopment to increase the accuracy of time ofprecipitation occurrence

AQ RAIN ACCUMULATION VALIDATION

RAIN EVENT – AUG 18/2012

AQ IFOV REPRESENTATION

• The validation has been conducted usingEDR WindSat data.

• 3B42 data was interpolated to WindSattime using same methodology than theAQ RA product.

• Verification of the rain events werecompleted using visual comparison andnormalized cross correlation

-1

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1

2

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INSTANTANEOUS 3B42 RR INTERPOLATED TO WINDSAT TIME

INSTANTANEOUS WINDSAT RR

NORMALIZED CROSS CORRELATION MATRIXNormalized cross-correlation reflects :• Shifting of 2 pixels

(50 Kms) in horizontal direction.

• Maximum correlation equals to 0.6026

Win

dSat

RR A

vg[m

m/h

r]AQ

RA

[mm

/hr]

SSS

[psu

]

AQ Orbit # 2 – Beam 2

Win

d Sp

eed

[m/s

]

RRRA03RA06RA09

RR Avg PrevWeekRR Avg Prev Month

AQHYCOM

WS NCEPSCAT WS